Ever since the first United States patent was issued in 1930 to Samuel Sadtler (U.S. Pat. No. 1,758,913) for a rubber and asphalt mixture for use as a road surface product, the asphalt industry has continued to devise new methods for the production of rubber modified asphalt cement (RMAC).
To date, some of the processes for producing RMAC include the addition of solubilized rubber crumb (U.S. Pat. No. 5,798,394, Meyers et al.) gelled crumb rubber (U.S. Pat. No. 3,891,585, McDonald), melted crumb rubber (U.S. Pat No. 5,492,561, Flanigan I) (U.S. Pat. No. 5,334,641, Rouse), mechanically sheared (U.S. Pat. No. 6,66,676, Rouse et al.), and/or acid treated asphalt (U.S. Pat. No. 5,095,055, Moran) for incorporating vulcanized rubber into asphalt. Memon (U.S. Pat. No. 6,444,731) teaches addition of a dispersion agent, such as furfural and/or vegetable oil) to the crumb rubber material, which is then heated at elevated temperatures that can be as high as 1500° C., to ensure the rubber is fully treated with the dispersion agent. The treated rubber is then added to hot asphalt, after which an activator (a Lewis acid that contains a trace of sulfur) and a micro-activator (phenyl formaldehyde resin) are added and mixed, to achieve a modified asphalt.
Although prior art processes have made some inroads in improved production of RMAC, the hurdle remains to find a way to devulcanize recycled vulcanized particulate rubber (RVPR) and incorporate it into the asphalt in a single step process. Such a process should not degrade the asphalt or the rubber through the use of high temperatures, require highly sophisticated equipment or release harmful toxins into the air.